Electrical Equipment Service

[jatrottpe]

Not sure if this is in the right forum. (and pardon the long windedness)

BACKGROUND
We recently brought a serviceman in from a major electrical equipment vendor to do some work on a 5kv metal clad switchgear lineup.

We have a full arc flash program in place (all equipment labeled with levels, boundaries, PPE, etc).

Our equipment is meticulously maintained (Full P/M program including breaker turn around, relay testing, cubicle cleaning, etc).

We typically can not de-energize large equipment without significant impacts. So we typically engineer methods to work in a manner that is as safe as possible, we have meetings with craft personnel and get there buy in on all work being done and mitigate as many risks as possible, we will write procedures were necessary and reivew all required PPE, (typically we do not include the pie in the sky type items, ie what if the unit blows up?, what if an earthquake strikes, or more than two concurrent failure items, etc) and if we can not mitigate them through safing off, PPE or procedures, we take the unit down to work the issue.

SCENARIO
We are having the manufacturer replace a defective design, MOC Switch rocker arm inside the control compartment cubicle of the switchgear. (another story for another time)

The breaker had been racked out and is out of the gear on a dolley.
The control voltage is shut off.
The shutters are closed, (there is no exposed bus or live circuits in the cubicle).

We have classified the work area as a NFPA 70E Hazard Risk category 1. Our requirements are for 1 Layer Nomex 4 cal/cm*cm.

We were under the impression that there is no reasonable cause of an arc flash in performing the work under the above conditions.

ISSUE
The vendor informed us that they can/will not do any work inside the control cabinet without the bus being de-energized, due to the possibility of an arc flash occuring. (It is fines work, so the 65 cal suit makes the job impracticle to perform). Since the gear is not the "Arc Flash Mitigation" type, the calculated boundaries apply around the whole gear and are not limited to within the gear during normal steady state operation, thus making the area surrounding the gear requiring arc flash PPE if the distance from the source of the arc flash to the gear is not less than the different calculated boundaries.
(During normal operating conditions and no work being performed on equipment, Walking into our substation buildings puts you in the Flash Protection Boundaries, the back of the gear to the wall behind puts you in the Restricted approach or limited approach boundaries, this interpretation by the vendor seems to be a bit extreme in our opinion.)


ANALYSIS/QUESTION
It appears that the vendors are taking the Easy way out, treating every facility and installation the same. Not allowing for sound engineering judgements to justify the types of work being done.

On the other hand, we are not so arrogant that we feel we are absolutely 100% correct and the vendors thinking has 0% merit. This incident has caused us to rethink our approach, however we (engineers, mgt, craft) are coming up with the same conclusions we did before.

Any thoughts?

 

[zog]

While this is a common maintenance practice for MV substation techs it is a unuique situation, I do this all the time, and have had this same arguement.

The arc flash boundary is only in effect when you are interacting with the equipment, could working on the control circuits in your 5kV switchgear be considered interacting, you could argue that either way, if you have electromechanical relays a mechanical shock could trip a breaker in the adjacent cubicle, so maybe they have a point, with solid state relays the odds are much less of that occuring.

My advice would be to calculate the actual Ei at the distance the work will be performed and wear the appropriate PPE for the Ei calculated. The 65 cal/cm2 calc was probally estimated at 18" or so, it is just a matter of playing around with the equations.

Or you can use the 70E tables which takes into account the chances of an arc flash event occuring, your example would most likely be a HRC 2 per the tables. Keep in mind that you are not supposed to use the tables because it is more convient or less restristive than your arc flash analysis results, but you can use them to justify your companies stance on the issue.

AS far as the shock boundaries go, the LAB and RAB only are in effect when there are exposed live parts, which there are none in your senario, so they are not an issue.

 

[jatrottpe]

Thank you for the response.

The gear in question was installed in 2006 and has solid state relays.
The work was mechanical in nature, the MOC switch mechanical lever hits a bolt on the switchgear structure, we have had a lever fail due to hitting the bolt head, we also have more than six other units that have visible stress fractures we are trying to replace.
All voltage sources (125vdc control, 120vac aux) in the compartment are de-energized (individual circuit breakers in compartment). This is one of the reasons we were using HRC-1 instead of HRC-2.

Our big issue is the fact that we have over 100 substations (circa 1957 thru 2007) and as such have probably one of everything in our yard, so what works on one, may not work on all.

PS
Our calcs for 2.4kv and up systems are based on 36" working distance. We standardized on 65cal suit and through relay settings have limited the calcualted arc flash to be under 65cal. (Thanks to a 480V, 3500kva transformer) To try and limit the choices, possibilities of mistake by our technicians, amount of PPE our guys need to account for, we have either nomex with Arc flash hood or 65 cal suit, Our policy has evolved and been revised a few times as new items keep coming up and I guess it will still evolve as these types of things rear their ugly head.

 

[jim dungar]

Our calcs for 2.4kv and up systems are based on 36" working distance. We standardized on 65cal suit and through relay settings have limited the calcualted arc flash to be under 65cal. (Thanks to a 480V, 3500kva transformer) To try and limit the choices, possibilities of mistake by our technicians, amount of PPE our guys need to account for, we have either nomex with Arc flash hood or 65 cal suit, Our policy has evolved and been revised a few times as new items keep coming up and I guess it will still evolve as these types of things rear their ugly head.

While it is laudable for you to chose 65 cal clothing, arc flash incidents involving more than 40 cal/cm? involve additional risks not covered by the FR rating of the clothing; energized work in these areas is be discouraged according to the NFPA (see the FPN of NFPA70E appendix D.8 and FPN No.2 to NFPA70E 130.7(10)). As a result many companies write their policies prohibiting energized work in areas with greater than 40 cal/cm? available.

 

[zog]

Sound like you are approaching this the right way.

Note: Anything >40cal should be labeled dangerous, they dont make a flash suit that can protect a worker from the pressure wave of an arc >40cal/cm2. This was a revision in the 2004 70E, following further arc blast testing.

 

[WDeanN]

Note: Anything >40cal should be labeled dangerous, they dont make a flash suit that can protect a worker from the pressure wave of an arc >40cal/cm2. This was a revision in the 2004 70E, following further arc blast testing.

Just a note of contention, and a personal pet peeve. NFPA 70E does not prohibit work above 40 cal/cm2. They understandably advise against it. I think the misunderstanding comes from reading the NFPA 70E Handbook, and not the actual code. We prohibit it at my location, but that is an internal safety rule. As such, Jim?s comment is more accurate:

?arc flash incidents involving more than 40 cal/cm? involve additional risks not covered by the FR rating of the clothing; energized work in these areas is be discouraged according to the NFPA (see the FPN of NFPA70E appendix D.8 and FPN No.2 to NFPA70E 130.7(10)). As a result many companies write their policies prohibiting energized work in areas with greater than 40 cal/cm? available.

 

[jatrottpe]

We are sensitive to the other issues associated with the IE over 40 cal (ie blast issues). I/we actually take this issue very seriously, not just to be in compliance with the code.
All our gear is secondary selective, so in some scenarios we have in effect double the calculated IE. We have developed procedures to de-energize one of the mains at the distribution voltage level, with instructions to operators to not start any large motors while the racking of breakers or other high HRC work going on. We utilize remote racking on our newer units. We have trained our entire process, mechanical and technical staff in our arc flash procedures and we had additional training for our operators who actually operate the equipment, all who work/operate on gear have their own arc flash suit w/fan.
Anecdote - About 2 months after we instituted our plant wide procedures, we had an arc flash. Our guys were following the procedures and the suit protected the electrician, other than getting the S scared out of him he was unscathed. We had absolutely zero grumblings from the rank and file about wearing the suits since, in fact we actually have made the requirements more stringent from feed back from our craftsman. If a policy is going to work, there has to be a cultural acceptance, not just a directive being followed.

Again thank you for your feedback.

 

[zog]

Just a note of contention, and a personal pet peeve. NFPA 70E does not prohibit work above 40 cal/cm2. They understandably advise against it. I think the misunderstanding comes from reading the NFPA 70E Handbook, and not the actual code. We prohibit it at my location, but that is an internal safety rule. As such, Jim?s comment is more accurate:

Touche'

I was basing that off the blue notes in the handbook, Jims statement is more accurate however after witnessing several arc flash tests >40 cal you wont catch me ever working in that environment.

 

[zog]

We are sensitive to the other issues associated with the IE over 40 cal (ie blast issues). I/we actually take this issue very seriously, not just to be in compliance with the code.
All our gear is secondary selective, so in some scenarios we have in effect double the calculated IE. We have developed procedures to de-energize one of the mains at the distribution voltage level, with instructions to operators to not start any large motors while the racking of breakers or other high HRC work going on. We utilize remote racking on our newer units. We have trained our entire process, mechanical and technical staff in our arc flash procedures and we had additional training for our operators who actually operate the equipment, all who work/operate on gear have their own arc flash suit w/fan.
Anecdote - About 2 months after we instituted our plant wide procedures, we had an arc flash. Our guys were following the procedures and the suit protected the electrician, other than getting the S scared out of him he was unscathed. We had absolutely zero grumblings from the rank and file about wearing the suits since, in fact we actually have made the requirements more stringent from feed back from our craftsman. If a policy is going to work, there has to be a cultural acceptance, not just a directive being followed.

Again thank you for your feedback.

What remote rack system are you using and why only on the newer breakers?

Also have you looked at Quick Trip ?

http://www.utilityrelay.com/QUICK-TRIP_Page.html

 

[WDeanN]

I was basing that off the blue notes in the handbook, Jims statement is more accurate however after witnessing several arc flash tests >40 cal you wont catch me ever working in that environment.

Me either. I feel funny just walking in front of some of them, after seeing some of the videos. I’ve just seen the “prohibited” myth presented too many times…

Also have you looked at Quick Trip ?
http://www.utilityrelay.com/QUICK-TRIP_Page.html

I’m not much of a fan of the maintenance switches. Too much room for error, or leaving it on/off when it should be otherwise. However, I talked with a sales rep over at URC a while back, and they may be adding a zone interlocking module to their capabilities, as well.

 

[WDeanN]

As a side note, zog, do you ever go off line? Every time I log in here, the little green light is on by your name. I even noticed it when I checked the site at night, from home a few times...

Maybe you're just following me..........

 

[zog]

Evryone likes to talk about "Risk" and when the arc flash boundary is in effect, I have a new view on this today.

Talked to a friend yesterday that had one of his employees injured from an arc flash that occured as he happened to be walking past a 480V MCC, he was just passing by when a operator (Remote) stopped the motor, the starter failed on opening. Luckly this facillity required FR clothing and safety glasses/hard hats, so his injuries were minor, but could have been bad.

 

[zog]

As a side note, zog, do you ever go off line? Every time I log in here, the little green light is on by your name. I even noticed it when I checked the site at night, from home a few times...

Maybe you're just following me..........

I just forget to log off when I am done, my wife is always asking me if she can close my "Geek" site.